Prior to the present invention, various methods were available for making symmetrical and asymmetrical triarylsulfonium salts. For example, P.A.Lowe, Chemistry of the Sulfonium Group, Volume 1, John Wiley, New York, 1981, page 13 and Trost et al, Emerging Synthetic Intermediates, Academic Press, London 1975, provide reviews of synthetic routes for synthesizing triarylsulfonium salts. Smith et al, U.S. Pat. No. 4,173,476, shows a procedure for preparing a triarylsulfonium complex using a mixture of diphenylsulfoxide, diphenylsulfide, and phosphorus pentoxide. Although procedures such as Smith et al provide complex triarylsulfonium salts, the 44% yield of the salt is relatively low, and the range of substrates which can be used is extremely limited. In addition, Smith et al's reaction mixture is heterogeneous due to the insolubility of the phosphorus pentoxide. Further, workup is complicated by the slow hydrolysis of the sticky mass of excess phosphorus pentoxide, products and starting materials.
In an improved procedure for making triarylsulfonium complexes, a strong acid, such as sulfuric acid, is used in combination with an oxidizing agent, such as peracetic acid and a dehydrating agent, for example acetic anhydride to produce in-situ, a mixture of a diarylsulfide and diarylsulfoxide. This mixture can be converted to the corresponding trirarylsulfonium acid complex followed by metathesis to the corresponding hexafluorometal or metalloid salt. Although effective results can be obtained using a strong acid, such as sulfuric acid, lower yields can be expected due to the sulfonation of the substrate as a competing side reaction.